The present invention relates to a control system for an internal combustion engine using a microcomputer and, more particularly, to an engine control system suitable for automobile gasoline engines.
The automobile engine, especially, an automobile gasoline engine, must satisfy stringent exhaust gas regulations and is required additionally to achieve sufficiently high performance. Therefore, in recent years, a control system for automobile gasoline engines has been available wherein various kinds of data representative of the running state of an engine, such as intake air flow rate for the engine and rotation speed thereof, are sequentially fetched, requisite control data for each cylinder is calculated on the basis of the fetched data, and the fuel supply amount and ignition timing are controlled independently for each cylinder on the basis of the control data. One may refer to examples of control systems disclosed in, for example, JP-A-58-185973, JP-A-59-49372 and JP-A-59-201972.
This type of control system needs data representative of the rotation speed of the engine, and in the prior art, a rotation speed derived from the period of a so-called reference angle position signal (REF signal) which is generated each time the crank shaft reaches a position of a predetermined angle of, for example, 180 degrees is used in common to cylinders as rotation speed data for calculation of engine control data.
The aforementioned prior art however fails to consider problems that the rotation speed of the engine contains irregular pulsations, detected data greatly differs depending on detection techniques and a delay in detection of the reference angle position signal which amounts to at least one period of the REF signal is inevitable. Therefore, when applied to a high-speed type engine having small rotational inertia, the prior art systems can not provide control data sufficiently reflecting differences in combustion state among cylinders, with the result that even control data independently prepared for each cylinder is used in vain to achieve sufficient suppression of roughness and satisfactorily optimum ignition timing control.